If your car has Blue & Me fitted you will probably need a cable to extend the existing B&M wiring so that it can be relocated out of the way somewhere (The B&M box is just behind the bottom half of the standard head unit, so if you install a true double din unit it'll have to move. The standard head unit is actually a single din unit with a double din front). You can't disconnect Blue&Me without having a permanently flashing odometer! Search on this forum for CTBLUEANDMELEA.
Also, if you have BOSE you might need another part to convert the output from the Pioneer into an input suitable for the BOSE amp.